1. Field of the Invention
The present invention relates to a main spindle apparatus of a machine tool for detachably coupling a tool holder for supporting a tool with the main spindle in such a manner that a position of the tool in a radial direction perpendicular to an axial direction of the main spindle can be controlled during the rotation of the main spindle.
2. Description of the Related Arts
Heretofore, in case of forming a tapered bore in a work piece, a tool such as a cutter coupled with a main spindle is moved in a radial direction perpendicular to an axial direction of the main spindle. Further, in order to change the tool, the tool is detachably coupled with the main spindle. Therefore, the machine tool has to be provided with a main spindle apparatus for detachably coupling the main spindle with the tool such that the tool can be moved in the radial direction.
For instance, in Japanese Utility Model Publication No. 62-161904, there is described a first known main spindle apparatus. In this main spindle apparatus, a clamp rod is biased by a belleville spring in a backward direction and a neck portion of a pull stud secured to a tool holder of taper shank type is held by a clamp ball such that the tool holder is prevented from being removed from a taper socket of the main spindle, wherein the control of the radial position of the cutter is carried out by slidably inserting a recess rod and a reciprocally moving rod into the clamp rod and pull stud.
In Japanese Utility Model Publication No. 61-40410, there is disclosed a second known main spindle apparatus having a similar construction as that of the first known main spindle apparatus, in which there is provided a means for engaging a correcting bar with a connecting rod.
Furthermore, in Japanese Utility Model Publication No. 61-28643, there is described a third known main spindle apparatus, in which a slider is held by a supporting block which is secured to a lower end of the main spindle by means of bolts and the radial position of the cutter is controlled by moving an operation rod in the axial direction.
In the first known main spindle apparatus, there are following problems.
(a) A mechanism for pulling the tool into the main spindle has to be provided, so that the construction becomes very complicated. PA1 (b) The tool is held only by a tapered portion, and thus mechanical strength of holding the tool is weak. PA1 (c) During the high speed rotation, the main spindle is liable to be unbalanced due to the deformation of the belleville spring, so that the precision of machining is reduced. PA1 (d) The recess rod and reciprocally moved rod are merely brought into contact with each other, but are not coupled with each other, and thus the outward radial movement of the tool is effected by the forward movement of the recess rod and the inward radial movement of the tool is performed by a driving force of a spring provided in the reciprocally moved rod. Therefore, in order that the reciprocally moved rod follows the movement of the recess rod against the sliding resistances of the tool holder and gear portions, there is required a very large spring force, so that a necessary force for driving the recess rod becomes also very large. PA1 (e) When the tool is secured such that its cutting edge is faced toward the axis center of the main spindle and the outer radial boring is carried out, if there is applied an outward radial force that is larger than the spring force, the tool is moved away from the axial center and the machining is no more possible. PA1 a main spindle having a male screw formed in an outer surface of one end portion of the main spindle; PA1 a clamping nut having a female screw which is engaged with said male screw of the main spindle and a plurality of clamping claws; PA1 a tool holder for supporting a tool movably in a radial direction perpendicular to an axial direction of the main spindle, and having a portion which is engaged with said clamping claws of the clamping nut; PA1 a first driving member arranged movably in the axial direction within said main spindle and having first and second end portions, said first end portion being connectable to a driving source for moving the first driving member in the axial direction; PA1 a second driving member arranged movably in the axial direction within said tool holder and having first and second end portions; PA1 a coupling means for detachably coupling said second end portion of said first driving member with said first end portion of the second driving member by moving said first driving member in the axial direction; and PA1 a converting means arranged in said tool holder for converting a movement of the second driving member in the axial direction into a movement of the tool in the radial direction.
In the second known main spindle apparatus, the radial movement of the cutting tool is controlled by engaging the correcting bar with the connecting rod, and thus the above mentioned problems (d) and (e) can be solved . However, when the engaging member is provided in the standardized conventional pull stud, the engaging member has to be very small, so that its mechanical strength becomes very small . If a diameter of the pull stud is increased in order to install a large engaging member therein, diameters of the belleville spring, main spindle and bearings have to be correspondingly large, and therefore the main spindle apparatus is not suitable for a high speed rotation . Moreover, it is necessary to provide a special cylinder for rotating the engaging member over 90 degrees . This results in the increase in the number of parts and the cost is liable to be high.
In the third known main spindle apparatus, the construction is rather simple, because only the operation rod is provided within the main spindle . However, the supporting block is secured to the main spindle by the bolts, and thus the tool could not be exchanged automatically. In a machining center, the tool has to be exchanged often, so that it is desired to utilize an automatic tool exchanger.